Define 1NF, including what constitutes atomic values.

• A. 1NF requires all attribute values to be atomic (indivisible) and each row to be unique, with column values of the same domain.
• B. 1NF allows nested relations and multi-valued attributes.
• C. 1NF requires duplicate rows.
• D. 1NF ignores domain consistency.

Answer: (A)

First Normal Form focuses on making every table a flat structure where each cell contains a single, indivisible value. This means no repeating groups or nested tables within a row, and every row represents a unique record. At the same time, each column should hold values drawn from a single defined domain, so the data in a column is consistent in type and meaning.

Atomic values are the essence here: a value that cannot be broken down into smaller parts within that column. If a cell were to hold multiple items, such as a list of phone numbers or an address concatenated with other details, that would violate 1NF. The usual remedy is to split the data into separate rows or create another table to represent the relationship, ensuring each cell stays atomic.

Seeing these pieces together, the option that states all attribute values must be atomic, that rows are unique, and that column values come from the same domain best captures what 1NF requires. It aligns with the idea that a relation is a set of unique tuples with consistent, indivisible data in each field.